Method of drying objects



Jan; 27. 1925- 1,524,567

w. J. PLEWS METHOD OF DRYING OBJECTS Filed Dec. 14, 1921 QZMM/INVENTOR A4 A TTORNEYS.

Patented Jan. 27, 1925.

UNITED STATES PATENT oFFl-cE.

J. PLEW S, OF NEW ROCHELLE, NEW YORK, ASSIGNOR OF ONE-HALF '1'0 W. SCOTT HUTOHINSON, F MOUNT VERNON, NEW YORK.

METHOD OF DRYING OBJ'EG'IS.

Application filed December 14, 1921. Serial No. 522,288.

To all whom it may concern.-

Be it known that I, WILLLAMJ. PLEWS, a subject of Great Britain, residing at New Rochelle, in the county of VVestchester and State of New York, have invented certain new and useful Improvements in Methods 9 of Drying Objects, of which the following is a specification.

-' This invention relates to a method of extracting fluid or liquid from, or drying, objects and is particularly applicable to objects and material where it is desired to remove the liquid, or a considerable portion thereof, without materially altering the original form, shape, or dimensions of the object or material.

My invention is particularly applicable to clay products in the manufacture of porcelain, tiles, brick, terra cotta, hollow tiles, porcelain insulators, earthenware, and the like. It is also applicable to the drying of the paste, or active material, for storage battery plates, also to cores for molds and various other objects and material where as aforesaid, it is desired to avoid any material change in the size or shape of the object or material during the drying process.

i This application is a continuation in part of my pending applications, Serial No. 340,- 386, filed November 24, 1919, and Serial No. 480,728, filed June 27, 1921, which relate particularly to the manufacture and treatment of storage battery plates and of the active material thereon, and to which the present invention is applicable. The presout application is more general in its scope,

and also relates particularly to the drying of clay products and to the new clay product produced by my improved process.

The drying of objects and material to which my invention is applicable, has commonly been done heretofore by drying in the open air, or by heating, or by causing a blast or current of warm air to be passed over or around the object or material. Any such process and particularly where the drying is slow, is expensive in the handling of the material and in the amount of stock in process of manufacture and space required; it furthermore results in an inferior product due to cracking, warping, or other distortion of the object and also is not of homogeneous structure throughout and is lacking in' strength. For example, in the manufacture of porcelain and other clay products, the former method of drying results in the above difficulties because the molded object is dried more-quickly at its surface than within the body of the object and even at and near the surface dries unevenly and ir regularly; also the subsequent drying within the body of the object occurs more or less 'une'venly and irregularly largely due to the formation of cracks at the surface and even causes cracks to be formed within or through the object. The resultant distortion of the object as a whole, its shrinkage, cracking, and lack of homogeneity, sets up internal strains and causes a lack of strength which even subsequent firing in a furnace will not remove. These difficulties of prior drying methods result in a large percentage of waste of material in the ordinary process of manufacture through breakage of the parts in handling or treatment during manufacture; and even the completed objects are objectionable and unsatisfactory in use owing to the distortion, shrinkage, internal strains and lack of uniformity in the completed articles.

. A particular example of these difficulties arises in the manufacture and use of porcelain insulators, such as insulating tubes for electrical resistance units, insulating tubes for wiring buildings and high tension insulators for transmission lines. Here it is not onl important to have an insulator of strength and homogeneous structure and which will be free from cracking or breaking, in handling, installation and when in use, but it is also desirable that the insulators for certain purposes shall be uniform in shape, and dimensions. Thus in the manufacture of tubular resistance units, on which the resistive conductor is wound on the outside of the porcelain tube, it is desirable to have all the tubes for a certain resistance and use to be uniform in size and of the same resistance. If all the porcelain tubes are uniform in shape and dimensions, they may be more convenientlywound with the resistive conductor so as to give a uniform resistance and will also properly fit into the structure or place in which they are intended for use.

One important object, therefore, of my invention is to provide a process of drying which will result in the production of objects which will be uniform in size and shape, homogeneous throughout their structure and of greatly increased strength compared with similar manufactured objects dried according to prior methods.

Another important ob'ect is to produce a process of drying whic will be rapid as compared with the many hours, days or even weeks required by. some prior methods with certain classes of objects. This results in reduced cost of manufacture and a large reduction of material on hand in course of manufacture for the same output, as compared with prior methods. Another important object which is articularly important in manufacturing c ay products and 1n the drying of the active material in battery plates and the like is the production of a product, after drying, which will be uniforml porous throughout its structure. The ro notion of this condition not only avoi s shrinka e, cracking and distortion of the shape 0 the object or material, but results in giving greatly increased strength in the final product. Another advantage,

in theproduction of clay products, for example, is that the shrinkage and drying is not only greatly reduced or substantially avoided as compared with prior methods, but in the firing of the objects in a furnace or kiln, the shrinkage occurring during the firing is also great y reduced or substantially overcome. These and other objects and advantages of my invention will be understood from the following description.

In applying my invention to' the manufacture of porcelain, for example, the molded object formed from a mixture, say

- of clay, flint and feldspar, is in a plastic condition and needs to be dried before placing in the firing furnace or kiln. My process is particularly applicable to the drying stage. chamber or receptacle adapted to be closed tightly and to withstand internal pressure and heat. After the chamber is closed a suitable fluid medium under pressure is admitted to the chamber and the temperature raised. As a convenient means of applying the desired temperature and pressure, I employ preferably a heated fluid pressure medium, for example, steam. Other heated gases may be used where preferable, as for example exhaust from an internal combustion engine, or any suitable gas, which will be inert as regards any objectionable effect on the object. When steam is used, it is preferably superheated.

The pressure in the chamber must be 'suflioient during the heating, to prevent material vaporization of the fluid in or near the surface of the object so as to avoid The molded object is placed in ashrinka e or crackin or irre lar va iization indiflferent ins of thfibject iii ch as occurs in air drying. That is, the pressure must at all times be approximately e ual to or greater than, the vapor pressure of the fluid in the ob'ect at the increasing temperatures to whic the object is'subjected. This will prevent any a preciable vaporization of the fluid from't e object. The introduction of pressure from an external source ma be done quickl and the heatin process t us ermitted to' e accomplishe quickly. en the pressure fluid introduced also heats the object, as in the case of steam or hot the pressure increases sufficiently rapidly to avoid the objectionable vaporization of the fluid from the object during the heatin process. The simultaneous introduction 0 ressure and heat in this manner may thus done convenientl and the tem rat-ure of the object and the pressure in the chamber may be made comparatively high rapidly. The more rapidl the pressure and temperature are raised, t e less will be the time required for this step of the, process, and the more quickly will the object be umforml' heated.

The amount of pressure required, the degree of temperature and also the len h of the heating will de end upon the particular character of the o ject or material treated and the results uired in a particular case; but the time required in this portion of the process is short. "Also in some cases during the pressure and heating process there may take place chemical changes in the material to a greater or less degree and in other cases there may be no chemical chan e or no appreciable chemical change in the material, thisdepending upon the nature of the object or material worked upon and the ingredients of which it is composed. The object or material may acquire a permanent set during this heating process, due to chemical changes or to physical changes, or the object may become set during the following portion of the process.

The pressure is now reduced, but this pressure must be relieved radually. The reduction in pressure is gradually continued until atmospheric pressure is reached. In some cases where it is desired to obtain a comparatively high degree of drying of the object or material, the article may remain in the vessel for a time at atmospheric pressure and in some cases a vacuum may be created in the chamber to a considerable degree for further drying of the article if esired.

During the gradual pressure reduction portion of the process, the decrease of pressure permits the fluid within the object or material to vaporize, not only at the surface but also throughout the body of the object. As the reduction in pressure continues, the vaporization continues, resulting in a uniform, gradual, continuous and comparatively rapid vaporization of the liquid contained in the object. This action in the case of clay products and in drying the active material of battery plates for example, results in producing a uniformly porous structure in the object or material, extending throughout the body thereof. The avoidance of uneven or irregular drying and the provision of pores uniformly through the mass for the passage of vapor from the object, produces a product which does not crack, war or become otherwise distorted or materia ly change its dimensions by shrinkage. It also produces an article of a homogeneous character having uniform strength throughout its parts and in which there are no appreciable internal strains.

The process may be repeated, for further drying of the object or article if desired or, as above stated, the object may be further dried or heated at atmospheric pressure or by the application of avacuum.

The provision of the uniformly porous condition in the object by the above drying, or dehydrating, process is particularly advantageous in the manufacture of clay products, because the subsequent firing in the furnace or kiln enables the chemical change and union of the ingredients tobe accomplished uniformly throughout the structure producing a final product of greatly increased strength over prior methods of drying, while at the same time avoiding internal strains. Also the shrinkage or distortion of the object which has heretofore occurred in the firing of objects dried by former methods, is largely reduced or sub stantially eliminated, because the object has a homogeneous structure when placed in the furnace or kiln and the heat of firing thus has a uniform effect throughout the body of the object. Also the length of time required in firing is reduced, because the object, being porous and homogeneous throughout, the vitrification may take place more uniformly and all parts are correspondingly vitrified in substantially the same length of time.

The accompanying drawing is a vertical cross section of one form of apparatus-for carrying out the above described process.

The size, form and arrangement of the apparatus will, of course, be adapted for the particular character of the objects or material to be dried or dehydrated by the above process. The drawing illustrates a chamber 1 having a, cylindrical wall 2 and end heads 3, the end heads making a tight joint with the cylinder and may be held in place in any suitable manner; and one or both of the end heads should be removable for permitting the introduction and removal. of the objects or material to be dried. In the present instance there are indicated tubes 4 to be which are supported by rods passing through them and which in turn are supported by a rack 5 which is removable from the chainber.-

Any suitable racks or supporting means for the objects may be provided to suit the particular requirements. The cylinder 2 is shown as having a jacket 6 which may be heated by exhaust gases, or from any suitable source of auxiliary heat, an intake pipe being shown at 7 and an outlet pipe at 8. The apparatus may also be covered by any suitable heat insulator as indicated at 9. An inlet pipe to the drying chamber is shown at 10 through which the superheated steam or other heated gas may be introduced to provide the pressure and heat required, and an outlet pipe from the chamber is shown at 11 with a valve 12 for gradually relieving the pressure and providing an exit for the gas and vapor, as above described. The other inlet and outlet pipes are also shown provided with valves 13. A pressure gauge 14: is connected with the chamber and a temperature indicating device 15 is also shown connected with the chamber so that the operator may know the pressure and temperature conditions in the'chamber at all times and regulate them as required.

It will of course be understood that the temperature and pressure required and the length of time required in the above process will depend upon the character of the object or material which is to be dried or dehydrated. In the case of dehydrating molded objects composed of a mixture of clay, flint and feldspar for the manufacture of porcelain, I have attained excellent results by using superheated steam and bringing it to a maximum pressure of from 50 to 200' pounds and at a temperature of about 550 F., the pressure and heating operation being acomplished Within about 5 to 15 minutes and the time during which the pressure is gradually reduced being carried out in about 1 to 2 minutes.

The product obtained by the above process in the case of clay products is, as above stated, uniformly porous and homogeneous in characteristics and the process avoids distortion, shrinkage or cracking, resulting in a new product not attained by rior methods.

Although I have describe my process with particular reference to the drying of clay products and particularly in connection with the manufacture of porcelain, yet my invention is applicable to the drying or dehydrating of other objects or materlals.

In some cases, it may be desirable to permit an exit, to some degree, of the heat and premure supplying medium while the pressure is being increased, or while being maintaineidhand thus 31 some cases obtlaain zmpre rap1 ryin an a more comp ete rymg where desira ble.

\Vhere I refer in the claims to objects or' material bein moulded, I intend to include material which is cast. or otherwise formed.

- I claim 1. The process of removing fluid from material which comprises subjecting the material to heat and external pressure, and gradually reducing said pressure.

2. The process of removing fluid from material which comprises subjecting the material to heat and external pressure at least substantially equal to the vapor pressure of the fluid at the temperature to which the material is heated, and gradually reducing said external pressure. p

3. The process of removing fluid from material which comprises subjecting the material to heat and external pressure greater than the vapor pressure of the fluid at the temperature to which the material is heated, and gradually reducing said external pressure.

4:. Theprocess of removing fluid from ma,- terial whleh-comprises placing the material in a closed chamber, applying heat and pressure to the material within the chamber, and gradually reducing the pressure.

5. The process of removing fluid from material which comprises placin the material in a closed chamber, app-lying heat and pres sure to the material within the chamber, said pressure being at least equal to the vapor pressure of the said fluid at the temperature to which said material is heated, and gradually reducing the pressure.

6. The process of removing fluid from material which comprises placing the material in a closed chamber, applying heat and pressure to the material within the chamber, said pressure being -reater than the vapor pressure of said flui at the temperature to which said material is heated, and gradually reducing the pressure.

7. The process of removing fluid from a moulded clay mixture which comprises placing the moulded clay in a closed chamber, applying heat and pressure to the moulded clay within the chamber, and gradually reducing said pressure.

8. The process of removing fluid from a moulded clay mixture which comprises placing the moulded clay in a closed chamber, applying heat and pressure to the moulded clay within the chamber, said pressure bein at least equal to the vapor pressure of fluid at the temperature to which said moulded clay is heated, and gradually reducing said pressure.

9. The process of removing fluid from a moulded clay mixture which comprises placing the moulded clay in a closed chamber, applying heat and pressure to the moulded clay within the chamber, said pressure bein greater than the vapor pressure of said flui at the temperature to which said moulded clay is heated, and gradually reducing said pressure.

10. The process of removing water from a moulded clay mixture which com rises placing the moulded clay in a closed ciiamber, injecting steam into said chamber and heating the moulded clay thereby under pressure of the steam, and gradually reducing the pressure.

11. The process of removin water from a moulded clay mixture which comprises placing the moulded clay in a closed chamber, injecting superheated steam into said chamber and heating the moulded clay thereby under pressure of the steam, and gradually reducing the ressure.

WILL AM J. PLEWS. 

